Sylvain Lebresne created CASSANDRA-16063:
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Summary: Fix user experience when upgrading to 4.0 with compact
tables
Key: CASSANDRA-16063
URL: https://issues.apache.org/jira/browse/CASSANDRA-16063
Project: Cassandra
Issue Type: Bug
Components: Legacy/CQL
Reporter: Sylvain Lebresne
The code to handle compact tables has been removed from 4.0, and the intended
upgrade path to 4.0 for users having compact tables on 3.x is that they must
execute {{ALTER ... DROP COMPACT STORAGE}} on all of their compact tables
*before* attempting the upgrade.
Obviously, some users won't read the upgrade instructions (or miss a table) and
may try upgrading despite still having compact tables. If they do so, the
intent is that the node will _not_ start, with a message clearly indicating the
pre-upgrade step the user has missed. The user will then downgrade back the
node(s) to 3.x, run the proper {{ALTER ... DROP COMPACT STORAGE}}, and then
upgrade again.
But while 4.0 does currently fail startup when finding any compact tables with
a decent message, I believe the check is done too late during startup.
Namely, that check is done as we read the tables schema, so within
[{{Schema.instance.loadFromDisk()}}|https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/service/CassandraDaemon.java#L241].
But by then, we've _at least_ called
{{SystemKeyspace.persistLocalMetadata()}}} and
{{SystemKeyspaceMigrator40.migrate()}}, which will get into the commit log, and
even possibly flush new {{na}} format sstables. As a results, a user might not
be able to seemlessly restart the node on 3.x (to drop compact storage on the
appropriate tables).
Basically, we should make sure the check for compact tables done at 4.0 startup
is done as a {{StartupCheck}}, before the node does anything.
We should also add a test for this (checking that if you try upgrading to 4.0
with compact storage, you can downgrade back with no intervention whatsoever).
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